The invention primarily concerns a measuring system with optical signal and energy transmission between an intelligent sensor head and a central measuring unit for medium-voltage or high-voltage systems or in mining. Furthermore, the invention relates to method therfor.
For measuring the operating voltage in medium- or high-voltage station control systems normally voltage transformers are used. According to the operating voltage of the station control system the isolation and turns ratio have to be chosen in order to decrease the operating voltage to an indicating voltage of less than 100 V which is suitable for measurement purposes. Depending on the respective task (billing measurement, line and apparatus protection technique, performance measurement technique) single-pole or two-pole isolated voltage transformers are used in very different forms of construction.
Voltage transformers generally make up a high share of costs for station control systems and station control instrumentations. They have large physical dimensions and have influence on the construction of the station control system. They are sensitive against excessive voltages and represent the weakest element of hardware in the construction of a station control system. Secondary connection lines between voltage transformer and protective relay or between voltage transformer and measurement unit can be considerably influenced by magnetic fields, ground leakage currents, short-circuit currents and interference fields, which often leads to a distortion of the measurement results.
DE 37 27 950 C2 discloses a device for performing voltage measurements in medium-voltage and high-voltage station control systems, which offers a complete substitution for usage of voltage transformers within the scope of performance measurement technique. The opto-electronic sensors used there enable an electrical and mechanical decoupling of measurement location and indication, they are insensitive to interference fields and excessive voltages and are also distinguished by small physical dimensions and relatively low costs. For performing voltage measurements as a phase comparison measurement, in particular two opto-elektronic sensors are provided which are connected at the supporting insulator with switching electrode. Furthermore, two opto-electronic sensors of ferroelectric type are provided which are each connected over optical wave guide with a remote situated transceiver unit and which are sampled simultaneously by these transceiver units by means of the reflection method. A phase comparison device is connected to both transceiver units whereas two comparators connected to both transceiver units convert the conveyed analog input signal into a square-wave signal. Two monostable multivibrators connected to the comparators generate short pulses from the square-wave signal synchronous to the zero crossovers of both phases. Finally, a sum counter is provided which is connected to the output of both multivibrators and counts simultaneously incoming pulses as a single pulse and counts incoming pulses with a delay as separate pulses. Devices for evaluation and indication of phase coincidence, phase opposition, lack of a phase distribution and functionality are connected to the outputs of the sum counter. In an alternative way of realization a series connection of a diode and a further capacitor is provided parallel to the capacitor between switching electrode and earth and a voltage dependent CMOS pulse generator is connected parallel to this. The outputs of the pulse generator are connected over a capacitor to the opto-electronic sensor of ferroelectric type, which is connected via optical wave-guide with a light transceiver with measuring amplifier. The measuring amplifier contains an element for converting the pulse frequency into a value appropriate for the input of a voltage measurement device, consisting of a digital-to-analogue converter or a frequency-to-voltage converter. In a device according to DE 37 27 950 C2 signal processing and evaluation is done remote from the measurement location, respectively centrally.
DE 38 24 000 C2 discloses a monitoring unit for protection against damage to pylons where sensors other than optical wave-guide sensors can also be used. In particular, at every foot of the pylon an optical wave guide, an infrared detector or a vibration detector is employed as a sensor and from there an optical wave guide is conducted to the monitoring device. In case of the optical wave-guide sensor a dismantled wave guide of loop type is conducted along a corner support foot of the pylon and, at the upper end of the monitoring area, passes into a twin-wire mantled optical wave-guide cable. This cable is conducted along a corner support of the pylon to a central monitoring device which is located in a metal housing within the upper third of the pylon on a cross beam of the pylon. Besides the central monitoring device, for every infrared detector and vibration detector a single monitoring device exists which is made up of an electronic module in a metal housing and is located at the upper end of the monitoring area in a corner support of the pylon. From there a single-wire optical wave-guide cable is conducted to the central monitoring device. While infrared or vibration detectors are integrated into the signal device, in the case of the optical wave-guide sensor its conductor only is inserted into the signal device. In the central device the optical signals transmitted from the single devices are converted and provided to the evaluation logic which, in co-operation with the task scheduler, forwards the alarm message via radio data transmission to an observation point. There a distinction of the signal devices, which triggered the message, is possible. The signal devices with infrared detector or vibration detector have a battery supply and the following components, which are in series arrangement: sensor, amplifier, filter, evaluation logic, light emitting diode and socket for the connector of the optical wave guide cable to the central device. Furthermore, a HP filter for suppressing unwanted temperature outputs is used for the passive infrared detector, whereas an active BP filter for frequency selection is used for the vibration detector. In the evaluation logic a decision is made whether there is an alarm case or not. In the monitoring device according to DE 38 24 000 C2 a signal pre-processing and evaluation is already performed at the measuring location.
DE 198 32 707 C2 discloses a combined current and voltage converter for outdoor switching stations with a semi-conventional voltage converter of a CC-, RR- or RC-divider type and an all-optical current converter in form of an optical wave guide loop surrounding the high-voltage conductor. Furthermore, a common converter evaluation device for both current converter and voltage converter is provided which has ground potential. When evaluating the signals from the voltage converter and the current converter, the measurement values of the single phases can thus be assigned to each other, and a phase-synchronous measurement of the single phases can be performed.
DE 195 43 363 C2 discloses a transducer arrangement for measuring currents and voltages in medium- or high-voltage systems comprising at least one current or voltage sensor for acquisition of measurement values, one coder for encoding of measurement values, one optical transmitter for transmitting and one optical receiver for receiving of the encoded measurement values, and at least one decoder for decoding of measurement values at the receiver location. For enabling an easy installation of the transducer arrangement in a medium- or high-voltage system as well as an adaptation to the respective measurement requirements without big efforts, the transducer arrangement consists of combinable modules with standardized interfaces. Moreover, at least one sensor module is provided with the current or voltage sensor, at least one transmitter module with the encoder and the voltage sensor, and at least one receiver module with the optical receiver and the decoder. The sensor module and the transmitter module are adapted to each other with respect to their physical dimensions and their connectors and they are combined mechanically to a high-voltage module, which guarantees an easy installation in the high-voltage system. In a preferred embodiment the sensor module for measuring DC or AC voltages comprises a voltage sensor in the form of a preferably frequency compensated ohmic voltage divider which is provided with a surge protector on the low voltage side. The transmitter module may comprise a voltage-to-frequency converter for generating a pulsed carrier signal as an encoder as well as an optical transmitter with at least a transmitter diode for converting the carrier signal into optical pulses. The receiver module accordingly comprises an optical receiver with a light sensitive receiver diode for converting optical pulses into an electrical pulsed carrier signal as well as a frequency-to-voltage converter as a decoder. Transmitter module and receiver module are both connected together with an optical wave-guide. Furthermore, the high-voltage module comprises an auxiliary energy supply unit for supplying the transmitter module whereas the auxiliary energy supply unit is supplied by the optical wave-guide.
DE 100 10 913 C1 discloses a device for monitoring the gas density of an insulating gas-filled high-voltage transmission line, which is separated into several line sections by partition walls, which comprises components placed in the vicinity of the partition walls for measuring the gas density in the line sections and transmitting of measurement results as well as a signal processing unit for receiving and evaluating the measurement results. In particular, the measurement components are supplied by a centrally located energy source containing a light source over at least one energy supply line in form of an optical wave-guide. The measurement components contains opto-electric energy converter for converting light into electric energy and several measurement components are connected in series with the light source over a common energy supply line. The energy supply line and the signal transmission line can also be combined in form of a simple optical wave-guide. The measurement component mainly consists of an energy conditioning unit, a computing unit and a sensor unit. The energy-conditioning unit is supplied with energy by an energy source containing a light source over an energy supply line in form of an optical wave-guide and an opto-electric energy converter. Depending on the configuration of the monitoring device the light source contains one or more laser diode modules each with a power of up to 500 mW. Furthermore the energy conditioning unit contains a capacitor, for example a low leakage current ELKO or an array of tantalum or ceramic capacitors, which stores the energy delivered from the energy source and if required provides it to the computing unit. The computing unit mainly comprises a microprocessor, which serves for controlling the sensor unit, acquisition and preprocessing of the values measured by the sensor unit and transmitting of the preprocessed measured values to the signal processing unit over a light emitting diode, a signal transmission line in form of an optical wave guide and an optical sensor. In the respective method for monitoring the gas density of an isolating gas-filled high-voltage transmission line, the measuring component is fed from the energy source with constant power during a wait cycle, then the gas density is measured by the measuring component, the measured value is transmitted to the signal processing unit and then the measurement component is reset to a wait state up to the next measurement.
Finally, DE 695 20 371 T2 discloses an optical-fiber interface system, wherein a regulation effects that the current fed to a laser light source is as low as admissible so that at the same time a remote interface and a process variable transmitter are provided with sufficient energy. In particular a first locally stationed microcontroller device is provided, which serves for adjustable supply of optical energy at a first output connector and serves for reception of digital encoded, optically transmitted information from the remote location at a first input connector of the microcontroller device. An analog transmit device is electrically connected to the first locally stationed microcontroller device and arranged in a way that optionally either analog or digital information or both at the same time can be conveyed to a local control system. A second microcontroller device is stationed in a remote location, i.e. remote from the first microcontroller device, and serves for receiving of analog and/or digital signals, which define the state of a process variable, like pressure, temperature, flow, motion, density or other parameters, which were captured by a remote process variable transmitter, and for conveying optical coded state information to a second output connector. An energy supply unit is coupled to the second microcontroller unit and the remote process variable transmitter and supplies them with electric energy. The energy supply unit contains an optical-to-electric energy converter with a second input connector. At least one optical fiber is connected between the first output connector of the locally stationed equipment and the second input connector of the remote stationed optical-to-electrical energy converter. The same or a second optical fiber is connected between the second output connector of the remote stationed microcontroller unit and the first input connector of the first locally stationed microcontroller unit. Furthermore, a unit that includes the first microcontroller unit initially conveys optical energy with an eye-safe lower value to the first output connector. The second microcontroller unit reacts to the reception of the eye-safe lower light energy value over the first optical fiber and transmits a start-up command over the fiber-optical link to the first locally stationed microcontroller device, whereby additional light energy above the eye-safe lower value is only delivered to the first optical fiber if it is properly connected between the respective output and input connectors. Furthermore, a light source energy supply unit exists locally which supplies a light source, like e.g. a gas laser, a laser diode or a LED with electrical energy, and the light source contains a device for modulating the intensity of the optical energy, which is conveyed to the first output connector. The first microcontroller unit also contains a first microprocessor for controlling the light source energy supply unit and the light source modulation unit. The first microprocessor receives energy status information from the remote stationed second microcontroller device, which enables a control, particularly a PI control (Proportional-Integral-control), of optical energy, i.e. the laser current which is provided from the local location to the remote location, in a “quasi-static operation” with a check of the laser voltage at regular intervals (status messages: message of six 8-bit bytes).
The above discussion of prior art acknowledges different measurement systems, which mostly contain a central signal processing unit and several electrical measuring components and which perform an optical transmission over optical wave guides of the measured values delivered from the measuring components. As such measuring have to meet high requirements with respect to operational safety, e.g. in monitoring of a high-voltage power switch, a safe capturing of measured values and a reliable fiber-optical data transmission is desirable. However, too little attention is paid to the fact that the constant activation of the laser diode for remote supply of the measuring component leads to a considerable shortening of the lifetime of the laser diode. Additionally, due to electromagnetic influences originating from the high-voltage system, particularly because of switching procedures at a high voltage level, interference signals in the optical signal transmission may cause malfunctions by clock displacement of the measured signals (measured currents respectively measured voltages). Even the fiber-optical interface system according to DE 695 20 371 T2 with its “quasi-static operation” only causes the current fed into the laser light source to be as low as admissible. Therefore, a fiber-optical measuring system is missing in practice, which has low power consumption and enables a safe optical data transmission. This is especially important because the industry manufacturing medium-voltage or high-voltage systems can be considered as a very progressive industry which quickly picks up improvements and simplifications and puts them into practice.
In contrast to known measuring systems, it is the underlying purpose of the present invention to provide such a measuring system that has low energy consumption and yet enables a safe optical data transmission.